Drag (or friction loss) reducing materials have been addressed extensively in the literature and in patents. Water soluble drag reducers have been used in hydraulic fracturing of subterranean formations, in pipelining of aqueous streams in plants and refineries, in storm sewers, firefighting hoses, sprinkler systems, etc. Oil soluble drag reducers have been used primarily in the transportation of hydrocarbon oils, such as crude oil, through long distance pipelines. Other uses have been proposed, particularly in plants and refineries. Certain uses in offshore petroleum production would be feasible provided that drag reducers, which are usually high molecular weight, viscous materials could be delivered to the locations of desired use.
According to this invention the pressure drop in a conduit flowing a viscous drag reducing material is greatly reduced by injecting into the periphery of the conduit a liquid material which is immiscible with the drag reducing material and of substantially lower viscosity in a sufficient amount to form a flowing layer of such liquid material on the inner walls of the conduit.
In one aspect of the invention the process is carried out to provide a supply of drag reducer without excessive pressure drop through a small diameter circular conduit which is normally used to provide low viscosity chemicals to subsea oil well completions, which may be substantial distance from shore.